1. Field of the Invention
The present invention relates generally to an asynchronous transfer mode (ATM) connection band control method and a control system. More particularly, the invention relates to an ATM connection band control method and a system effectively using connection bands which respective ATM circuit ports have.
2. Description of the Related Art
In FIG. 9, the conventional ATM connection band control system includes an input circuit 1, an input buffer control portion 2c, an ATM switch control portion 3c and an output buffer control portion 4.
The input buffer control portion 2c includes a buffer accumulation memory 21c for accumulating input cells before feeding to an ATM switch, an input buffer function portion 22c performing writing control of ATM cells to a buffer accumulation memory and queue management of the buffer, a usage parameter control (UPC) portion 23c monitoring whether a traffic of a user in communication exceeds a band declared upon switched virtual connection (SVC) setting demand or not, a connection admission control (CAC) portion 24c controlling whether a demand is to be admitted or not upon reception of signaling of connection setting demand for new SVC of constant bit rate (CBR), a real time variable bit rate (rt-VBR), a non-real time variable bit rate (nrt-VBR), a buffer control memory 26c storing parameter or data necessary for operation of the input buffer function portion 22c and the usage parameter control (UPC) portion 23c, and a circuit interface control portion 20c interfacing the input buffer function portion 22c and the input circuit 1 for feeding the input cell to the ATM switch.
The ATM switch control portion 3c includes an ATM switch 30c performing switching of the ATM cell, CPU 31c performing central control process of overall system and a main memory 32c for residence of operation program or data necessary for operation of CPU 31c. 
FIG. 10 is a detailed block diagram showing a buffer control memory 26c relating to the connection band of SVC of FIG. 9 and its peripheral control portion. The buffer control memory 26c includes a memory 261c storing band data per declared connection upon SVC setting demand necessary for control operation of the usage parameter control (UPC) portion 23c, a memory 263c storing connection band data of SVC of CBR, rt-VBR, nrt-VBR, and a memory 264c for storing data necessary for other connection admission control, such as available band of ATM circuit port and so forth.
Only connection band data of SVC of currently established connection is present in the buffer control memory 26c for performing connection admission control and connection band control.
In this case, the connection band control and the connection admission control is performed for acquiring necessary connection band in first-come-first-set order without considering connection band of preferential SVC when the SVC of established connection issues setting demand. Therefore, when connection of the preferential SVC is not yet established and issue setting demand for connection later, the SVC setting demand is not always admitted and can be rejected until the necessary band is released in certain remaining band of the ATM circuit port.
On the other hand, even when the connection of the preferential SVC is established, if the preferential SVC is deleted once, the connection band acquired unconditionally is released. Therefore, even when the preferential SVC issues setting demand again, there is not guarantee to acquire connection band. If other SVC sets the connection earlier, the setting demand may be rejected until the necessary band is released in certain remaining band of the ATM circuit port.
In the foregoing conventional ATM band control method, the first problem is that, in acquiring of the connection bands of each SVC of the CBR, rt-VBR, nrt-VBR requiring fixed band, the connection admission control (CAC) performing control on the basis of the band information of those actually established connection to acquire the band for those established connection at earlier timing for finite connection bands of each ATM circuit port. However, judgment is not made whether acquiring of band has to be done preferentially or not.
The second problem is that there is not means for preliminarily registering data for setting the band of the connection to be preferentially assigned without actually establishing connection and making judgment upon establishing connection.
The third problem is that when connection for SVC having high preference (preferential SVC) among SVCs is temporarily released for some hindrance to open the band, if the preferential SVC is recovered from hindrance and the preferential SVC demands resetting of connection and connection setting demand for other SVC having low preference (non-preferential SVC) is done at earlier timing, since connection setting of the non-preferential SVC is performed normally, there is no guarantee for permitting resetting of the preferential SVC. Therefore, whether resetting of connection is successful or not simply depends on remaining band of the ATM circuit port.
On the other hand, the fourth problem is that there is no means for performing control for ensuring and guaranteeing resetting of connection band for the preferential SVC when the connection band of the SVC having high preference, such as CBR or the like is temporarily deleted and the band is opened, and when the connection setting demand is issued by other SVC having lower preference while the connection of the preferential SVC is deleted. The connection band is inherently acquired in order to demanding of setting irrespective of preferential order. Therefore, for the SVC having high preference while not used constantly, connection has to be maintained irrespective whether the connection is used for communication or not to constantly occupy the connection band.
The fifth problem is that even when the SVC having high preference actually occupies the connection band constantly, the band may be used for the SVC of ATM category service which does not require fixed band, such as available bit rate (ABR), unspecified bit rate (UBR) and so forth as long as not cell flows in the connection. However, in the prior art, even when the connection is not actually used, an idle data is transmitted in CBR, the band acquired by CBR may not be released unless the setting of connection is actually deleted.